Communication networks in which communication components are connected to one another via data lines are being used instead of circuit-switching communication networks to an increasing extent. In this case, the communication components are often integrated into data networks which operate on the basis of the Internet protocol (IP networks), which is why such arrangements are also called Voice Over IP (VoIP) networks. In this context, the communication components may be arranged at any geographical location in the network. They transmit the audio signals digitally in the form of numerical information concentrated into data packets, known as voice data packets. For the purpose of interchanging the voice data packets, each communication component has an associated unique network address which is used to address each packet for interchange.
Besides communication components which perform the functionality of terminals known from circuit-switching communication, for example IP telephones, the VoIP communication networks also contain communication components with central functions which can be used alternately or simultaneously by single or a plurality of other communication components. A central communication component of this type, often also referred to as a server component, may provide a directory of all communication terminals, known as client components, which can be reached in the network, for example. If a first client component needs to set up a communication connection to a second client component, the first client component can retrieve from this server component the data which are required to set up the connection, primarily the network address of the second client component. A central server component of this type is frequently also referred to as a “gate keeper”. Other central server components, such as voicemail servers, gateways as a link to circuit-switching communication networks, conference facilities and the like, likewise provide central services in the packet-switching network.
The document “The Gnutella Protocol Specification V 0.4”, published on the Internet, discloses a method with which communication components on the Internet can be used to find other communication components for the purpose of interchanging files with them. In this case, however, the data interchange takes place not using a central server component or “gatekeeper”, but rather directly between the communication components. Networks which provide direct data interchange between communication components without a superordinate entity are called Peer-to-Peer networks. The communication components which comprise both client and server functionalities are frequently called “servents” in the literature.
In the Peer-to-Peer network based on the Gnutella specification, each communication component—which is a PC in this case—holds files ready for interchange with other communication components. In order to be able to interchange data, a searching communication component requires the network address of another communication component which holds the sought file ready for retrieval. To this end, the searching communication component first of all sends a first search message, the “ping”. The communication components which receive a “ping” search message of this type respond to the searching communication component with a hit response, the “pong”. This hit response contains the network address of the responding communication component and also the number of files provided by this communication component for interchange. In the next step, the searching communication component sends a second search message “query” to a limited selection of those communication components which have responded to the “ping” search message with a “pong”. This second search message already contains the file name of the file which is being sought. If a communication component receives a second search message “query” but does not itself hold the sought file ready for interchange, it forwards this search message to other communication components in the network whose addresses it has ascertained by means of a “ping” method which has already been carried out in the past, for example. If the communication component can provide the desired file for interchange, however, then it responds to the second search message “query” with a second hit response “query hit”, as a result of which the searching communication component can initiate the file transfer using commands defined in the Internet protocol.
The document US 2002/0073204 A1, Dutta et al. “Method and system for exchange of node characteristics for data sharing in peer-to-peer data networks” shows a packet-switched network containing communication components (in this case: computers) in which the computers interchange files with one another. In this arrangement, the files are sought and transferred on the basis of the Gnutella protocol. In this context, the user of a computer is shown characteristic information about another computer which has been found, this information relating firstly to the access parameters for the computers found and secondly comprising information about the files which are stored on these computers and can be used for file interchange. This information is shown to the user, so that the user can then decide whether a connection to the computer found needs to remain for the purpose of file interchange or whether this connection is to be cleared down.
When a client component requires the services of a server component of a particular type, there are often a plurality of server components of this type available in packet-switching networks. The client component stores a table which contains, arranged according to type, every accessible server component with its network address and the other information required for access. For each type of server component, one of these components is marked in the table as “default component”, that is to say as that component which is contacted first. If this default component is not available or cannot provide the adequate service features, then the next communication component is selected from the stored table in a defined order and is contacted. This process is repeated until a suitable, sufficiently powerful server component which is available at this time has been found.
The known packet-switching communication networks have been found to have the drawback that various server components of the same type are always having to be contacted in succession in a previously defined order. When adding or removing new client and server components, extensive administration processes are then required in each case.